Gloss is based on the interaction of light with physical characteristics of a surface. It is the ability of a surface to reflect light into the specular direction. The factors that affect gloss are the refractive index of the material, the angle of incident light and the surface topography. It is relatively easy to lower the gloss of a material by deliberately roughening a material's surface; in contrast, it is relatively more difficult to increase a material's gloss if the surface quality has reached its practical limit.